Helenus was the son of King Priam of Troy and Queen Hecuba in Greek mythology, twin brother of the prophetess Cassandra. Cassandra, who had been given the gift of prophecy by Apollo, taught its secrets to Helenus; however, he was believed by others, unlike Cassandra who had been cursed not to be believed by anyone, even though her prophecies always came true.

Helenus participated in the Trojan War and was part of the forces led by his brother Hector. Towards the end of the war and after Paris had died, Helenus was one of the people vying for Helen's hand, the other being his brother Deiphobus. Eventually, Helen was given to Deiphobus, and an angry Helenus retreated to Mount Ida, where he was later captured by Odysseus. Still bitter, Helenus revealed a way to capture Troy to Odysseus; if Greeks stole the Trojan Palladium, brought the bones of Pelops to Troy, and managed to persuade Philoctetes and Neoptolemus to join the Greek side, they would definitely win the war.